Difficulty tuning

Medium: min subset deductions 2

A Medium grid must force at least this many two-clue subset moves. Raise for meatier Mediums.

Hard: min overlap deductions 2

A Hard grid must force at least this many two-clue overlap moves (plus at least one subset move).

Extreme: min what-if deductions 2

An Extreme grid must force at least this many what-if moves: assume a square, watch a clue break. The deepest logic in the game.

Extreme: min chain depth 2

At least one what-if must need a chain this long (in counting steps). 1-step chains feel like overlap moves; 2+ guarantees a genuinely deep moment. Capped by MAX_WHAT_IF_FIRINGS .

Insane: min either-way deductions 0

Insane grids always exceed Extreme's chain cap. Raise this to additionally demand either-way moves: pivots where both hypotheses survive yet agree on another square.…